Obviously, it all depends on your interests. While the art classes are probably amazing as Johnson says, they simply aren't for me. Just explore courses which sound like they have the potential to be interesting, and you may find a new passion.
If you can't find something which really jumps out at you in the regular course listings, make sure to check out the UCollege. It's a continuing education / professional studies school through wustl which allows students to enroll in a class or two. It typically has some more offbeat courses, such as glassblowing, which has gotten some good reviews.
In terms of practicality or usefulness, I'm sure that a few intro level finance/econ/business classes could help many, and comp sci may play a role in quite a few areas of work. Or possibly even a foreign language if you plan on spending time with people who speak that language.